Currently, defects in fabricated components (e.g. wafers) can be detected by comparing a target component of a fabricated device to reference components of the fabricated device. Inspection systems accomplish this by taking images of the target and reference components for comparison purposes. In particular, detecting the defects often involves performing two separate comparisons to generate two separate results, one comparison being between the target component and one of the reference components and another comparison being between the target component and the other one of the reference components. Any similarity between the two separate comparison results is generally used as an indicator of a defect in the target component.
Prior art FIG. 1 shows traditional layout for a wafer having a plurality of target components in a column 102, each being a same pattern modulated (i.e. amplified) by a different combination of parameter (e.g. focus (F) and exposure (E)) values, and further having a plurality of reference components in columns 104, 106 situated on either side of the column of target components and each being a nominal (i.e. not modulated) version of the same pattern. Thus, for any particular one of the target components in column 102, a reference component from column 104 and a reference component from column 106 may be used for detecting defects in the particular target component (see box 108). While the reference components are shown as being adjacent to the target component, this is not necessarily always the case. For example, in other wafer configurations the reference components for any particular target component may be those closest, but not necessarily adjacent, to the particular target component.
Unfortunately, traditional methods for performing the above described defect detection involve techniques that introduce inaccurate results. For example, as described above, the target components are modulated in an effort to amplify defects. This amplifies both defects and non-defects in the target component. However, the reference components are traditionally nominal. The modulation of only the target component then causes like structures in the target and reference components to appear different when there is in fact no defect. Thus, the number of defects traditionally identified can be overly high, which limits the ability to discern actual defects from falsely identified defects.
Prior art FIG. 2 shows an example of the effect of traditional defect detection methods where modulation of only the target component is employed. In FIG. 2, as the modulation is increased for the target component, the size of each part of the target component (including defects and non-defects) also increases, thus causing differentiation between the target and reference components on a part-by-part basis regardless of actual defect. As shown, at higher modulation the difference image resulting from the comparisons includes additional differences than at lower modulations. Existing patents disclosing the above described prior art techniques include U.S. Pat. Nos. 8,213,704 and 6,902,855, the descriptions of which are incorporated by the reference in their entirety.
There is thus a need for addressing these and/or other issues associated with the prior art techniques used for defect detection in fabricated components.